414 



MOLLUSCOIDEA 



PHYLUM V 



commonly recurved, hut is sometimes bifurcated. Shells plicate and their structure 

 abundantly punctate. Silurian to Permian. 



Rhynchospira Hall (Fig. 627, C, D). Eostrate, radially plicate shells with 

 a short curved hinge-line ; apex truncated by a circular pedicle opening. 



Dorsal hinge-plate like 

 that of Trematospira. 

 Spirals with from six 

 to nine volutions. 

 Jugum V-shaped, ex- 

 panding apically and 

 terminating pos- 

 teriorly in an oblique 

 edge. Shell structure 

 punctate. Devonian 

 and Lower Carboni- 

 ferous; North Amei'ica 

 and Europe. 



Homoeospira Hall 

 a linear cardinal process 



Pig. 027. 



.-1, B, Pti/chospira ferita (von Buch). Devonian ; Gerolstein, Eifel. i/j. 

 C, D, Rhynckospira salteri (David.). Silurian ; Wenlock, Shropshire. C, In- 

 terior of dorsal valve. D, Median vertical section through both valves, 3/j 

 (after Davidson). 



and Clarke. Like the last, 

 separating the crural plates, 

 in an acute stem. Silurian ; 



having 



but differs in 



Jugum not apically expanded, but terminating 

 North America. 



Ptychospira Hall and Clarke (Fig. 627, ^, B). Like Rhynchospira, but with 

 a few angular plications. The jugum has a long, simple process passing 

 outward between the coils to near the inner surface of the ventral valve. 

 Devonian to Lower Carboniferous ; North America and Germany. 



Retzia King {Trigeria Bayle). Resembling Rhynchospira externally. The 

 ventral umbonal cavity has a split tube. The single process of the jugum 

 terminally forked. This genus formerly contained all shells having a retzioid 

 exterior. At present, however, but a single species is admitted. Devonian ; 

 Europe. 



Hustedia Hall and Clarke. Externally like Eumetria, 

 but with coarse plications, and internally with a split 

 tube, as in Retzia. Spirals and jugum similar to those 

 of Eumetria, but with fimbria and spinules respectively. 

 Upper Carboniferous and Permian ; America, Europe, 

 India and China. 



Trematospira Hall. Transverse Rhynchospirae. Silu- 

 rian and Devonian ; North America. 



Para2;?/5ra Hall and Clarke (Fig. 628). Like Trematospira, 

 but with the fine, simple ribs covered with very delicate, 

 short, hair-like spines. Devonian ; North America. 



Eumetria Hall. Elongate terebratuliform shells with 

 numerous fine radiating striae. Hinge - line short. 

 Dorsal hinge-plate very complicated. Jugum similar 

 to that of Retzia, but the terminally bifurcated process 

 is extended backward at an abrupt angle, and termi- 

 nates just in front of the apices of the primary lamellae. 

 Shell structure punctate. Lower Carboniferous ; North 

 America and Europe. 



Acambona White. Carboniferous ; North America. 



Fig. 628. 



Parazyija hirsvta (Hall). 

 Devonian ; Louisville, Ken- 

 tucky. ^, Shell of the natural 

 size. B, Same with dorsal 

 valve partly broken open, 

 showing spiralia. (.', hinge- 

 line of ventral valve, enlarged 

 after Hall). 



